1. Field of the Invention
The present invention relates to a wireless power transmission unit that can transfer energy from a power transmitting section to a power receiving section by a non-contact method. The present invention also relates to a device including a power receiving section to be used in combination with such a wireless power transmission unit and to a wireless power transmission system.
2. Description of the Related Art
Currently, power is supplied to various electronic devices ordinarily via wires (or cables). Such a wired power supply is advantageous in terms of power supply stability and safety precautions against electric shock because electric power is supplied while being confined in the wire. However, if an electronic device is connected to an AC outlet with a wire, then the portability of that device is much limited. On top of that, wired power transmission not just would give an untidy appearance but also could catch someone or something with the wire and make him, her or it stumble on it. Furthermore, since the AC outlet and the end of the wire are connected together via metallic contacts, those contacts should always be kept waterproof and dustproof as well.
Thus, to overcome with these issues with the wired power transmission, more and more people are paying increasing attention to wireless power transmission for supplying power to various electronic devices by a non-contact method. As methods for realizing such wireless power transmission, a conventional electromagnetic induction method can naturally be used. But a method that uses resonant magnetic coupling has also been proposed in United States Patent Application Laid-Open Publication No. 2008/0278264-A1 (see FIGS. 6 and 11, in particular), which will be referred to herein as “Patent Document No. 1” for convenience sake. According to the resonant magnetic coupling method, resonant mode coupling between resonant antennas is used to realize longer-range and higher-efficiency power transfer than the conventional electromagnetic induction method. They believe that particularly if a resonant magnetic field is used, influence on surrounding organisms would be reduced compared to a situation where a resonant electric field is used.
Japanese Patent No. 4318742 (which will be referred to herein as “Patent Document No. 2” for convenience sake) discloses an exemplary application of a wireless power transmission unit that uses the resonant magnetic coupling. According to Patent Document No. 2, a tertiary coil is provided between a primary coil for transmitting power and a secondary coil for receiving the power, thereby transmitting a huge amount of power to the secondary coil with even more efficiency. That is to say, the tertiary coil “relays” the power between the primary and secondary coils. If the distance between the power transmitting resonator (or coil) and the power receiving resonator (or coil) is substantially fixed in this manner, the power transfer efficiency can be maximized just by choosing the best installation position for the relay resonator and the best resonant frequency.
In a wireless power transmission unit with a relay resonator such as the one disclosed in Patent Document No. 2, however, the position of the resonator that receives the power wirelessly (i.e., the power receiving resonator) should be substantially fixed.
It is therefore an object of the present invention to provide a wireless power transmission unit in which the position of the device that receives the power being transmitted can be determined more flexibly.